I have used bar-ends on a couple of my builds, Vis...
Road oriented build
(Note these are shorter width bars than an MTB)
And here is a similar setup on MTB width Handlebars
On this second example, I wired only the hall effect throttle function on the barend placed thumb throttle parallel with the hall effect thumb throttle on the main handlebars.
Personally I find these barends to be the bees knees (read that as very good
), particularly the dual throttle setup on the MTB widh bars where I can easily swap down to the handgrips for concentrated handling situations, and swap up to the barends for longer distance comfort, plus the added benefit of being able to rest ones wrists by changing positions... the ergonomic geometry of having ones wrists and hands in-line on the barends seems to apply a lot less strain for longer distances/time, than using straight handlebars.
For the road build (top pic) I ended up doing away with the throttle on the handlebars, just running the one on the bar-end... for tricky or slow speed stuff, I tend to have my left-hand (non-throttle side) down on the bars so I can easily grab the brake (set up as rear brake).
On MTB width, using the bar ends feels a little like driving a truck, but in a good way wide armed position and very easy to control. Again in braking situations bringing the left hand back down to the handlebars from the bar-ends to control the rear brake is pretty intuitive, and makes transitioning the right (throttle) hand down to the bars very easy.